The spectrum of activity of macrolides, including erythromycin, covers most relevant bacterial species responsible for upper and lower respiratory tract infections. 14-membered ring macrolides are well known for their overall efficacy, safety and lack of serious side effects. Erythromycin however is quickly degraded into inactive products in the acidic medium of the stomach resulting in low bioavailability and gastrointestinal side effects. Improvement of erythromycin pharmacokinetics has been achieved through the synthesis of more acid-stable derivatives, for example, roxithromycin, clarithromycin, and the 15-membered ring macrolide azithromycin. However, all of these drugs, including 16-membered ring macrolides, present several drawbacks. They are inactive against MLSB-resistant streptococci (MLSB=Macrolides-Lincosamides-type B Streptogramines) and with the exception of azithromycin, weakly active against Haemophilus influenzae. Furthermore, the resistance of Streptococcus pneumoniae to erythromycin has increased significantly in recent years (5% to above 40%). There is a high percentage of cross-resistance to penicillin among these isolates, with a worldwide epidemic spread of 10-40% in some areas.
There is, therefore, a clear need for new macrolides that overcome the problem of pneumococcal resistance, have good pharmacokinetic properties and acid stability while continuing to be active against H. influenzae. 
Currently there is a new medical need due to an increasing prevalence of community acquired Methicillin-Resistant Staphylococcus aureus (CA-MRSA) in skin and soft tissue infections as well as nosocomial acquired MRSA. MRSA is a particular type of the bacteria that has developed resistance to many antibiotics, including methicillin, making it difficult to treat. Previously, MRSA infection was a problem mainly for patients treated in hospitals. Now, we are seeing MRSA in the general community, creating a tremendous need for new antibiotics with an improved safety profile and more convenient administration for use in hospitals as well as in community settings. The growing problem of bacterial resistance to many existing drugs also necessitates the development of new antibiotics to fight the battle. Current macrolide antibiotics, including erythromycin A, clarithromycin, and azithromycin have been successfully used in the treatment of respiratory tract and skin and soft tissue infections. Macrolides are generally safe and well tolerated. However, extensive clinical use of macrolides has resulted in the rapid emergence of macrolide resistance in staphylococci, streptococci, and enterococci. Current macrolide antibiotics are not active against the majority of MRSA isolates.
Improving activity of macrolides against MRSA isolates are the focus of this invention in addition to improving Haemophilus influenzae activities.
These new macrolides will be ideal candidates for drug development for skin and soft tissue infections and in upper respiratory tract infections (“URTI”) and lower respiratory tract infections (“LRTI”).